[mycroft]

Yesterday I saw a Costco tire shop was offering a nitrogen inflation service for tires (e.g., fill a tire with compressed nitrogen gas instead of normal "air"; a mixture of nitrogen, oxygen, etc.)

The claim was made that you'd get better mileage, tires might last longer, etc. Pure nitrogen might be lighter than compressed air, which might get you a bit of a mileage savings. But on the whole, what do people think?

 

[Phoenix]

Nitrogen in Tires

Probably the main advantage is that nitrogen is inert and displaces oxygen. This would prevent oxidation of steel and rubber from inside the tire. Also, I believe nitrogen is heavier than air, so it probably would not lighten the tires. Even if you filled them with helium, there probably isn't enough gas volume to make a noticeable difference.

Adding nitrogen may increase tire life a little, but I think this may be a marketing gimmick. Nitrogen isn't new; if this really works, it seems like someone would have thought of this about 50 years ago.

Does Costco charge extra for filling tires with nitrogen?

 

[mycroft]

Nitrogen has atomic number 7; Oxygen is 8. If I remember correctly, that means nitrogen should be a bit lighter. That doesn't mean it's light enough to make a difference.

I didn't ask whether they charge extra, but my assumption is they would.

 

[rpm]

Nitrogen has atomic number 7; Oxygen is 8. If I remember correctly, that means nitrogen should be a bit lighter. That doesn't mean it's light enough to make a difference.

As I recall, air contains more nitrogen than oxygen anyway, doesn't it?

rpm

 

[Daniel]

Air is mostly nitrogen. Using nitrogen instead of air avoids the water vapor in air, and supposedly the tires do not... errrmm, now I forget what it is they're not supposed to do when filled with nitrogen. But it has nothing to do with weight. They use it in racing cars. I am skeptical of any great advantage with car tires. Oh, yeah. I think nitrogen changes pressure with temperature a bit less than air. Probably because of the water vapor, which can condense or evaporate within the tire. (???)

The place I have always bought tires always uses nitrogen, for no extra charge. Of course, when necessary to pump them up I use air. In any case, air is something like 80% nitrogen, so it cannot hurt your tires. I would not pay extra for it.

 

[melgish]

If you put compressed nitrogen into your tires, won't your car get 'the bends' if you go up hill to fast? :shock:

 

[SkipHuffman]

Nitrogen has atomic number 7; Oxygen is 8. If I remember correctly, that means nitrogen should be a bit lighter.

And carbon is 6. I don't see too many charcoal brickettes floating in the air. Atomic number and density are at best loosely tied.

Nitrogen weighs 1.2506 kg/m3 dry air is 1.225 kg/m3

All five tires combined probably contain well less than a cubic meter of air. So replacing air with nitrogen saves about 9g, about as much as a dime and a quarter together. You can probably save that much mass by vacuuming regularly.

 

[Daniel]

Nitrogen weighs 1.2506 kg/m3 dry air is 1.225 kg/m3.

That's fine if you live in the desert. Otherwise, where are you gonna get dry air? In fact, I think if you have dry air you don't need nitrogen. I think the whole point of nitrogen is if it's pure there's no water in it. Pure oxygen or helium would work as well, but nitrogen is cheaper.

And by your figures, air is lighter than nitrogen.

I still think we should all get really big tires, and fill them with helium, so we'd not only be able to get 50 to 60 mpg, we'd be able to fly.

 

[Phoenix]

Nitrogen in Tires

By the way, don't put oxygen in your tires. Pure oxygen probably increases the rate of oxidation and deterioration of both the rubber liner and and the steel reinforcing bead and radial belts. There may also be a remote possibility of spontaneous combustion and explosion.

These are probably remote possibilities; but if it isn't a good idea to put butane/propane in tires (aerosol flat repair in a can), then pure oxygen can't be much better.

 

[vincent1449p]

Nitrogen in Tires

Nitrogen has been used on giant off-highway tires, on aircraft tires, and on racing tires for many years.

Air is about one-fifth oxygen, and oxygen, especially at high temperatures and pressures, is a very reactive element. When oxygen reacts with things, the process is called oxidation. When oxidation is extremely rapid, the process is called “burning.” That’s one reason nitrogen is used in off-highway and aircraft tires. These tires run so hot they can actually catch on fire. Nitrogen doesn’t support combustion, so nitrogen-filled tires don’t add fuel to the flames. And, nitrogen helps prevent slower forms of oxidation too.

Air migrates through rubber. Tires can lose 2 psi per month as a result of air passing through their sidewalls – like a balloon that shrivels up, but much slower. And, when oxygen passes through rubber, it can come into contact with steel cords, causing them to rust too. Between aging rubber and corroding steel cords, oxygen reduces retreadability.

While both nitrogen and oxygen can permeate rubber, nitrogen does it much more slowly. It might take six months to lose 2 psi with nitrogen, compared to just a month with air.

The air around us is full of water vapor. Water vapor in compressed air acts as a catalyst, accelerating rust and corrosion. Water vapor also absorbs and holds heat. And, when it changes from liquid to vapor, water expands tremendously in volume. So, tires inflated with wet air tend to run hotter and fluctuate in pressure more.

Hope this helps.

Cheers!

 

[SkipHuffman]

Re: Nitrogen in Tires

While both nitrogen and oxygen can permeate rubber, nitrogen does it much more slowly. It might take six months to lose 2 psi with nitrogen, compared to just a month with air.

Let me see if I am understanding correctly.

If I just keep refilling my tires with regular air I will slowly increase the partial pressure of nitrogen in the tire.

Also as things oxidise, that will remove gaseous oxygen from the air in the tires. Lets see, rust is FeO. <counts on fingers> That makes rust 25% oxygen by weight. About 250g oxygen in the tyre air, so you could convert 750g of iron to rust. Call it 175g per tire. That could be bad.

Also we need to consider that water vapor. Ok. H20 is a smaller molecule than O2. So it should diffuse through the rubber faster and the air should slowly dry out.

But hold on a second. N2 is smaller than O2 as well, so it should filter out faster than the oxygen. So the tyre air should slowly increase in partial pressure of oxygen.

Ok, I am really confused now. Can you point me to a link or article that discusses this?

Thanks,

Skip

 

[moocatdog]

Re: Nitrogen in Tires

Ok, I am really confused now.

As was I, until I started filling my tires with beer.
Drive happy,
Moo

 

[BIF]

Re: Nitrogen in Tires

Ok, I am really confused now.

As was I, until I started filling my tires with beer.
Drive happy,
Moo

I'm imagining a blowout now, making splashing sounds and scaring the hell out of the driver behind you!

 

[Victor]

If you put compressed nitrogen into your tires, won't your car get 'the bends' if you go up hill to fast? :shock:

Or is that Helium which makes the Navi sound like Donald Duck?

 

[jshore]

And carbon is 6. I don't see too many charcoal brickettes floating in the air. Atomic number and density are at best loosely tied.

Not quite so fast. Gases are different than solid or liquid forms of matter. For two "ideal gases" at the same temperature and pressure and volume, the number of molecules is in fact the same...and thus the the molecular mass is what matters. The molecular weight of an oxygen molecule is 32 and of a nitrogen molecule is 28 (both are diatomic molecules). Now, they are not precisely "ideal gases" but probably close enough at typical temperatures and pressures near to atmospheric to preserve the relationship of oxygen being a little heavier than nitrogen. (At very high pressures or very low temperatures, the molecules get closer together and the details of their size, shape, and interactions start to matter more so the deviations would become more pronounced.)

At any rate, I agree with your conclusion that any weight difference between air and nitrogen in your tires is way too small to matter.

 

[patrickg]

Dry nitrogen is a good fill for tires. Non-reactive, cheap, and slightly better thermal characteristics than air. If only your tires were less permeable, helium would probably be the superior choice as it is as inert as nitrogen but has superior thermal properties albeit at a higher price.

Hey Moo, is that draft or bottled, fresh or recycled?

Why not run a small percentage of inert or benign liguid in the tires, like maybe SLIME. Won't that help dynamically ballance the tires while you drive?

Pat

 

[vincent1449p]

SkipHuffman wrote:

Can you point me to a link or article that discusses this?

The article can be found at this link:
http://www.trucktires.com/us_eng/library/publications/periodicals/RealAnswers/03v8iss3/ra8.asp

Some more links:
http://auto.howstuffworks.com/question594.htm
http://www.toyo.com.au/tech_info11.html
http://www.mtdealer.com/t_inside.cfm?action=art_det&storyID=1207
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6,470,923.WKU.&OS=PN/6,470,923&RS=PN/6,470,923
http://www.tirelast.com/id5.html
http://www.prairiebizmag.com/article.asp?id=401

Your question has prompted me to search for a scientific explanation.

http://wine1.sb.fsu.edu/chm1045/notes/Gases/Diffuse/Gases09.htm
"The effusion rate, r, has been found to be inversely proportional to the square root of its molar mass and a lighter gas will effuse more rapidly than a heavy gas."

We know the molar mass for N2, air and O2 are 28, 29 and 32 respectively. So, N2 should actually effuse faster than air and O2.

http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14253029/gotomsg/14254472.cfm#14254472
"According to van der Waals equation for the behavior of non-ideal gasses, the a constant for N2 is 1.39 vs. 1.37 for N2/O2 mix (standard air). The b constant shows even less of a variation: 0.0391 for N2 vs. 0.0.0342 for the mix. It should be noted that the terms are both linear in the equation.
Also, plotting the PV/RT vs. pressure for 1 mole of gas shows that one must be in the pressure ranges of 100 atmospheres before appreciable differences in expansion behavior are noticed.

Given this, one would have to dismiss the arguments provided above, except perhaps the oxidizing effect provided by O2."

Some more opinions:
http://www.cartalk.com/content/columns/Archive/1997/September/05.html
"Their claim that nitrogen keeps your tire pressure more constant is actually correct. But their reasoning is wacko. It has nothing to do with diffusion of air through the rubber.

Seriously, you can keep your tire pressure constant enough for street and highway driving by simply checking it periodically."

http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14314827/srt/pa/pging/1/page/2.cfm
"Local tire store charges $6 a tire to fill with Nitrogen. Tech I know get a laugh every time someone goes for it. Says it the easiest money the store makes."

http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14397986/srt/pa/pging/1/page/2.cfm
"Unless you are racing, Nitrogen is just another scam. Industry site shows that a dealer must inflate approx. 100 tires a month to make the units pay for themselves.... read: sales pitch."

Any thoughts?

Vincent

 

[patrickg]

You pretty well covered the waterfront up to about 20 miles inland!

My comments re N2 being a good tire fill were not related to the inflated (pun intended) prices reported. N2 is a good tire fill. The hucksters prices are ludicrous but that goes to prove P.T. Barnum was right when he said there was a sucker born every minute.

When cigarette lighters used lighter fluid (Ronsonal or whatever brand) rather than butane I wasn't a smoker but laughed a lot at the price of a can compared to the cost of a gallon of benzine.

Yeah, what is the difference between calimari and squid? About $5 a pound!

Here is how Baja off roaders fill a tire when required to do it in the dirt away from mechanical services (or at a Mexican tire shop unequipped to deal with large tires):

With tire mounted but the beads not sealed you spray ether (starting fluid) or pour some gasoline in the tire and throw a match at it. The resulting explosion inflates the tire and seats the bead. Might take a few tries to get the fuel/air ratio right for the uninitiated. Pretty spectacular at night for the uninitiated (or most anyone else.) The resulting tire fill of fuel vapors, a bit of liquid gasoline perhaps, smoke, etc. can't possibly promote longivity.



Pat

 

[SkipHuffman]

SkipHuffman wrote:

Can you point me to a link or article that discusses this?

"Unless you are racing, Nitrogen is just another scam. Industry site shows that a dealer must inflate approx. 100 tires a month to make the units pay for themselves.... read: sales pitch."

Thank you for all the sources. Interesting reading. I am going to attempt an executive summary.

Advantages of pure nitrogen vs air for tire filling.

Some components of air are detrimental.
A) Oxygen. Oxygen breaks down internal tire components. This can reduce the tire life in extended highway use tires, such as truck tires, This effect is probably not applicable to typical passenger car usage.
B) Water vapor. In typical usage water in a tire may change state from liquid to vapor making pressure maintenance difficult. Water vapor can also act as a catalyst increasing oxydation rate.

Are these worth the extra cost? I kind of doubt it. I don't expect to get 150,000 miles out of a set of tires so the first one does not apply. As far as the second. Diligent maintenance can substitute.

Still it would seem that trying to get the lowest partial pressure of water vapor would be worthwhile. When would be the best time of day to get dry air? Beginning of the day or end of the day? Cool day or warm day? Dry day rather than a humid day would seem to make sense. Is there anything you could put in the tire to absorb water vapor? One of those dessication packages that are in many shipped packages? I keep a few grains of rice in my salt to keep it flowing. Would the same be advisable in a tire?

 

[patrickg]

Rice and water in the tires of a Japanese car. So if you run them hot it steams the rice and then what? Should you put Soy Sauce in too? How about ajinomoto?

Pat